GRAPHICAL REPRESENTATION OF DATA

         Classified data can be represented  by a variety of graphs in order to give a visual picture of the distribution.

          Histogram, frequency polygon,frequency curve, ogives and pie-diagram are some of them.

HISTOGRAM

      Histogram is the most accurate graph that represents a frequency distribution. In histogram the scores are spread uniformly over the entire class-interval.The class interval is marked on the x-axis and the frequencies on the y-axis.

            

FREQUENCY POLYGON

       In frequency polygon, we mark the mid-point of each class on the x-axis and the frequencies on the y-axis. After plotting all the points, we join them by line-segments. We complete the polygon; that is, we close it, by joining it to the x-axis.

         Frequency polygon gives a less accurate representation of the distribution, than a histogram, as it represents the frequency of each class by a single point, not by the whole class-interval.


FREQUENCY CURVE

     The frequency polygon consists of sharp turns, and ups and downs which are really not in conformity with actual conditions. To remove these sharp features of a polygon, it becomes necessary to smooth it.

       No definite rule for smoothing the polygon can be laid down. It should be borne in mind that the curve is as smooth as possible and does not, in any way, sharply deviate from the polygon.

        In order to draw a satisfactory frequency curve, we need, first of all, to draw a frequency histogram, then the frequency polygon and ultimately the frequency curve.